Beginning Python - From Novice to Professional

84 CHAPTER 5 ■ CONDITIONALS, LOOPS, AND SOME OTHER STATEMENTS
>>> values = 1, 2, 3
>>> values
(1, 2, 3)
>>> x, y, z = values
>>> x
1
This is particularly useful when a function or method returns a tuple (or other sequence or
iterable object); let’s say that you want to retrieve (and remove) an arbitrary key-value pair
from a dictionary. You can then use the popitem method, which does just that, returning the
pair as a tuple. Then you can unpack the returned tuple directly into two variables:
>>> scoundrel = {'name': 'Robin', 'girlfriend': 'Marion'}
>>> key, value = scoundrel.popitem()
>>> key
'girlfriend'
>>> value
'Marion'
This allows functions to return more than one value, packed as a tuple, easily accessible
through a single assignment. The sequence you unpack must have exactly as many items as the
targets you list on the left of the = sign; otherwise Python raises an exception when the assignment
is performed.
Chained Assignments
Chained assignments are used as a shortcut when you want to bind several variables to the
same value. This may seem a bit like the simultaneous assignments in the previous section,
except that here you are only dealing with one value:
x = y = somefunction()
which is the same as
y = somefunction()
x = y
Note that the preceding statements may not be the same as
x = somefunction()
y = somefunction()
For more information, see the section about the identity operator (is), later in this chapter.
Augmented Assignments
Instead of writing x = x + 1, you can just put the expression operator (in this case +) before the
assignment operator (=) and write x += 1. This is called an augmented assignment, and it works
with all the standard operators, such as *, /, %, and so on: